Why does an AVR development board draw much more than the MCU sleep-current figure?

Separate MCU current from whole-board current. Debug interfaces, USB bridges, LEDs, regulators and external sensors may remain powered. Check where the current is measured and whether the board provides an approved measurement configuration. The relevant schematic can explain a large difference without any firmware fault.

Check enabled clocks and peripherals, wakeup frequency, floating inputs and current through pull resistors. A pin held against a pull-up consumes current even while the core sleeps. Also check for back-powering through connected interfaces; removing only the main supply does not necessarily isolate a device.

Capture a complete wake-sample-sleep cycle and calculate average current from charge over time. Distinguish measurement burden and range-switching artifacts from real behavior. Compare the MCU conditions with the datasheet's voltage, temperature and enabled features, then decide whether the application budget concerns the chip alone or the assembled node.